1. Field of the Invention
This invention relates to an improvement of an AC driven gas discharge panel, particularly to a novel combination of electrodes and a dielectric layer in a gas discharge display panel of the self-shifting plasma type.
2. Description of the Prior Art
As an example of a gas discharge panel, an AC driven plasma display panel having a matrix type electrode arrangement is well known. However, such matrix plasma display panels have a drawback, namely, a complicated driving circuit is required in order to address individual discharge cells in the discharge gap at the intersection points of the electrodes arranged transversely in the horizontal and vertical directions on the two substrates. In addition, the cost of such driving circuits drastically increases with an increase in the size of the display panels. Thus, a "self-shifting plasma display" type gas discharge panel providing a discharge spot self shifting function was developed to simplify the driving circuitry.
Examples of such self-shifting plasma display panels providing various kinds of electrode arrangements are described in U.S. Pat. No. 3,944,875, U.S. Pat. No. 3,775,764, U.S. patent application Ser. No. 810,747, filed June 28, 1977, now U.S. Pat. No. 4,185,229 and U.S. patent application Ser. No. 813,627, filed July 7, 1977, now U.S. Pat. No. 4,190,788. The abovenoted U.S. Pat. No. 3,944,875 and both of the abovenoted applications are assigned to the same assignee as that of the present application. Self-shifting type display panels are basically composed of plural groups of shift electrodes connected to plural bus conductors for defining a shift line of discharge cells and write electrodes for defining write discharge cells. However, in such self-shifting plasma display panels, it is essential that only the data input to the write discharge cells be accurately shifted along the shift line. A discharge panel in which the discharge along the shift line is not based on such a data input would be worthless.
When actually operating such a self-shifting plasma display panel, an abnormal discharge occasionally occurs at a position not related to the desired discharge cells. This is not observed in the case of matrix type panels. Such incidental abnormal discharges will disturb the data in the panel, interfering with the display operation. Moreover, if such an abnormal discharge occurs often, the abnormal discharge may break down the dielectric layers, thus seriously reducing the life of the display panel.
The applicants of the present application have considered the various aspects of the abovenoted problem with respect to self-shifting plasma display panels and have determined the cause of such a problem, namely, an incidental abnormal discharge in a display panel results from an undesirable accumulation of charges on the discharge surface. In other words, in an AC driven gas discharge panel of the self-shifting type, a dielectric layer is normally used for coating the electrodes. This layer is generally composed of a glass film having a thickness of about 20 .mu.m and is fabricated by heating, at about 600.degree. C., a low melting point glass powder which has been coated on the electrodes by either printing or spraying techniques. However, in the case of such a dielectric layer formed of a low melting point glass film, bubbles generated by the electrode material during the heating process do not all dissipate completely to the outside of the film. Thus, some bubbles remain in the glass film. In addition, the low melting point glass material itself includes, in some cases, particles which are not melted perfectly and therefore remain in a solid state. Moreover, during the heating process, the low melting point glass material is shaped outwardly at the upper part of electrode, thereby causing the thin film layer to become thinner and, in the extreme, the electrode is exposed. Therefore, the dielectric layer is likely to have substantial differences in its dielectric coefficient as well as other differences in the electrical characteristics due to the abovementioned bubbles, particles and differences in the film thickness. On the other hand, when the abovementioned variations in the electrical film thickness exist along the shift line of a self-shifting type plasma display panel, (on the shift electrodes or between them), the moving charges are unequally accummulated in such areas during the shifting operation. Thus, a difference in the amount of accumulated charges occurs on the display surface, and when the magnitude of such a difference increases due to the repetition of the shifting operation, the abnormal field caused by this accumulated charge, in conjunction with the shift voltage, induces an avalanche phenomenon in the area adjacent to the accumulated charge area. This avalanche phenomenon causes the incidental abnormal misfiring as noted above. If such an accumulation of charges occurs in the thinner part of the dielectric layer, particularly severe discharges may occur. These discharges result in the thermal distortion of the dielectric layer and eventually cause the dielectric layer to break down. Concerning this point, in the case of a matrix type gas discharge panel which allows for only the fixed display of data, unequal accumulation of charges due to the movement of charges does not occur and therefore the aforementioned problem of abnormal discharges does not become important, (even in the case of a dielectric layer consisting of a low melting point glass film). However, in the case of a self-shifting type gas discharge panel, if such abnormal discharges occur even at a single point along the shift line, all the data passing such a point is destroyed, thereby rendering the panel unusable.